Measurements have historically been made on cutting sample or core samples either in the field or in the laboratory. Estimating mineralogy of conventional rocks (containing no hydrocarbon) using FTIR is an established technique. In this measurement, a library of spectra of standard minerals is recorded first, and then the spectrum of a rock is fitted to a linear combination of standards, with the fitted weights proportional to the abundance of each mineral. In favorable cases, this procedure can be extended to produce a simultaneous measurement of mineralogy and kerogen content by recording the spectrum of a standard kerogen and adding that to the library of standard spectra; for example, mineralogy and kerogen content have been measured in sediments using diffuse reflection FTIR data and in Green River oil shales using transmission FTIR data following this procedure.
Limited information has been collected by FTIR or visual inspection of formation solids under a microscope, especially cuttings with residual drilling mud solvents. More involved analysis have not been selected because of the time and cost for equipment and low likelihood of return of useful information. For example, FIG. 1 shows how an FTIR analysis may be distorted by the presence drilling mud fluids. Also, core samples may undergo more sophisticated analysis, and core samples do not have the same exposure to drilling fluids that cuttings samples undergo.
Separately, some references have methods based on interpreting variations in the FTIR spectra of kerogens from gas shales and oil-bearing shales to estimate properties of the kerogen. The properties typically measured are the kerogen type (reflecting the organic material from which the kerogen was formed) and maturity (reflecting the extent of alteration of the kerogen due to thermal processes). However, those methods require isolating the kerogen from the rock, typically by digesting the minerals using acid. Therefore, those methods provide no estimate of mineralogy.